Summary: The transplantable lines of prenoplastic, hyperplastic alveolar nodules will be used to study the nature of immune reactivity to an emerging tumor. Mice bearing these lines will be treated with various carcinogens (viral and chemical) which have been shown capable of influencing the conversion of pre-neoplastic lesions to frank neoplasia. The immune responses (cell-mediated immunity, blocking factors, lymphocyte-dependent antibodies) directed against nodules and tumors will be assessed by microcytotoxicity assay. In addition, the ability in this system of immune cells to stimulate tumor cell survival in vitro will be investigated.